Better error message for Null and 'sym singleton types.

Null and 'sym are not legal as singleton types because the underlying
values are not stable. They are rejected now outright instead of issuing
a cryptic "X is not stable" error message.

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/neg/singletons.scala b/tests/neg/singletons.scala
index 3bf7ee050..e4c6db060 100644
--- a/tests/neg/singletons.scala
+++ b/tests/neg/singletons.scala
@@ -2,4 +2,8 @@ object Test {
   val a: 42 = 43  // error: different constant
   val x = 42
   val z: 42 = x   // error: x is not final
+
+  val n: null = null // error: Null is not a legal singleton type
+
+  val sym: 'sym = 'sym // error: Symbol is a legal singleton type
 }